1. Field of the Invention
The present invention relates to data storage devices. More particularly, the present invention relates to rotating disk magnetic data storage devices.
2. Description of the Prior Art and Related Information
Rotating disk magnetic data storage devices, commonly referred to as disk drives, have undergone dramatic improvements in data storage capacity and data access times in recent years. At the same time, high performance portable computers have become increasingly prevalent. These require a high data storage capability in a compact environment. The constraints imposed by portable computers, as well as the decreasing footprints of desk top personal computers, have increased the need for high performance disk drives having compact dimensions; i.e., disk drives having a compact "form factor."
In order to provide a compact form factor high capacity disk drive, the major disk drive components must be carefully integrated into the disk drive housing. In particular, the principal mechanical and electromechanical components of the drive must be integrated together in a compact environment encased by a substantially airtight housing. These components and housing are typically referred to as the disk drive head disk assembly (HDA).
Of the basic components of the HDA, the actuator, which supports the read/write transducer heads, and the actuator motor are perhaps the most critical for achieving the rapid access times desired for modern disk drives. A "voice coil" actuator/actuator motor design is presently preferred for most modern high performance disk drives. In such a design, the actuator is pivotally mounted and has a "voice coil," in the form of a coil of wire, attached to the end of the actuator opposite the magnetic read/write heads. This voice coil is configured inside a magnet assembly in a manner such that energization of the voice coil causes an electromagnetic interaction with the stationary magnets to pivot the actuator about its mount to thereby rotate the magnetic read/write transducers in an arc across the data tracks on the disk surface.
Although voice coil actuators provide rapid access times and the potential for high data storage densities, problems are presented by the essentially free motion of the voice coil and actuator. That is, the voice coil and attached actuator are unconstrained by any mechanical motor components and, in response to an energizing current in the voice coil, will pivot freely in response to the force between the magnetic field induced in the coil and the permanent magnet. It will thus be appreciated that if a suitable braking force is not applied, the voice coil and actuator may pivot the magnetic transducer heads completely off the disk surface. Alternatively, the heads may crash into the spindle in the center of the disks if not restrained.
In normal operation, such a braking force will always be applied once the magnetic transducer heads have been moved to the desired data track on the disk surface. Where a power failure occurs, however, or an error occurs in the reading of position information (e.g., off the disk surface), it is possible that the actuator and attached transducer heads can overshoot the destination track and potentially move off the operational region of the disk surface. Additionally, when the drive is turned off, or is inactive to save power in absence of a command from the host computer, no current will be applied to the voice coil. In this state, due to the free pivoting of the actuator about its mount, the actuator and attached read/write heads may be moved off the disk surface by a disturbing force, such as jarring of the disk drive.
Accordingly, it is necessary to provide some means to prevent the voice coil actuator from rotating off the disk surface. Additionally, some type of a latching mechanism is needed in order to prevent the voice coil motor and transducer heads from moving about when the drive is turned off or otherwise not actively maintaining the actuator and heads at a desired position.
One conventional means for restricting the motion of the actuator employs simple mechanical "crash stops." These are typically some type of cushioned piece, provided on either end of the voice coil angular range. These cushioned stops limit the movement of the voice coil while reducing the shock provided to the actuator and transducer heads. One type of conventional latch mechanism in turn employs a mechanical latching structure which has a detent or catch which the voice coil engages.
Such mechanical latch structures and cushioned crash stops are suitable for disk drives where the space is not severely constrained. In modern very compact disk drives, however, the distance over which the voice coil must travel to engage the mechanical latch can be significant, since the portion of angular travel of the actuator arm during which the latching occurs corresponds to usable space on the disk surface. In modern applications where both high density and compact size are required, travel ranges during latching of as little as 50 mils. may result in significant lost data capacity. Similarly, unnecessary travel in the crash stops reduces otherwise useful disk surface area which may be used for data storage.
An additional consideration for very compact disk drives relates to the mounting mechanism for the actuator assembly. The actuator assembly must be free to pivot so as to move the transducer heads attached thereto readily from track to track in an accurate manner. In compact disk drives, this requires a very secure and compact mounting structure which is nonetheless easy to assemble during the manufacturing process. Furthermore, the circuit wiring which connects the read/write magnetic transducer heads to the disk drive read/write and servo electronics must not interfere with the precise rotational motion of the actuator. Furthermore, it is highly desirable to have the wiring detachable from the actuator assembly to allow replacement or repair of the actuator assembly in a relatively straightforward manner.
An additional consideration, which becomes increasingly significant for compact disk drives, is the need to keep the air in the disk drive housing relatively free of dust particles and other contaminants. In particular, in high performance disk drives the flying height of the transducer heads may be lower. As a result dust or other contaminants can more readily interfere with the head/disk interface, causing the heads to "crash" or otherwise interfering with the reading/writing of data onto the disk surface. Additionally, in order to maintain high data capacity while reducing disk size for modern compact disk drives, it is necessary to increase the data storage density of the magnetic media on the disk surfaces. This further renders the disk surface susceptible to data loss due to contaminants which may enter the disk drive housing and settle on the disk surface. Additionally, portable computers expose the computer and disk drive incorporated therein to a wide variety of environments where high levels of dust or other contaminants may be present. As a result, the disk drive must be provided in a housing which is sealed to prevent dust or other contaminants from entering the disk drive compartment.
In conventional disk drives, a gasket is typically employed between the upper and lower sections of the housing to provide a substantially airtight seal to the disk drive housing. Although this approach can be effective, space must be made for the gasket at the junction between the two sections of the housing. This in turn requires additional thickness for the housing walls, which can add undesired weight and size to the overall disk drive housing. This added weight and size becomes increasingly unsatisfactory for compact disk drives required for laptop computer applications. Additionally, the use of a gasket creates problems during assembly of the disk drive since the gasket is an unsupported piece which is not well suited for precise and rapid assembly. Furthermore, various components in the HDA are sensitive to electromagnetic interference and external electromagnetic fields may partially penetrate the HDA through the gasket.
Accordingly, a need presently exists for a compact disk drive head disk assembly which avoids the above-noted problems.